WRF-based assessment of the Great Lakes' impact on cold season synoptic cyclones

Synoptic events in December are studied with regard to the Great Lakes' influence on extratropical cyclones using the Weather Research and Forecasting (WRF) model. Here, four selected events are arranged into two pairs of comparisons: strong events (2006, 2009) versus weak events (2008, 2013); traversing events (2008, 2009) versus bypassing events (2006, 2013). For each case, the land surface model in WRF is initialized with two different configurations: the control run with real land coverage and the no-lake run in which the lakes are replaced by land. The control simulation shows that the WRF model exhibits a good performance in reproducing precipitation, sea-level pressure and air temperature. Comparisons between control and no-lake runs among these cases indicate that the lake-air temperature gradient, inducing vertical heat flux, is most prominent in the weak bypassing event (case 2013), while lake-land roughness contrast contributes to the low-level moisture convergence. The Great Lakes' impact generally strengthens the cyclonic system near the surface but is sensitive to the background flow. This effect becomes much more significant for the development of cyclones with colder atmospheric conditions, suggesting that the meso-to-synoptic scale interaction should be taken into account when considering the Great Lakes' influence.